This invention relates generally to electronic measuring systems and more specifically to an ash level meter for a fixed-bed coal gasifier.
In the operation of a fixed-bed coal gasifier, it is necessary to maintain the ash level at the prescribed elevation. If the level drops too low, grate burnout is likely to occur. If the level rises above a nominal optimum height, then the devolatilization, gasification, and fire zones become shortened with subsequent loss of conversion efficiency and over temperature at the gasifier outlet. To control the ash level, the grate is rotated at a speed/duty rate such as to maintain the nominal ash level, but control is dependent upon the availability of a dependable and relatively accurate means of measuring the ash level.
It has been the practice to provide thermocouples in the arm of the bed stirrer to monitor the temperature profile of the gasifier bed. The motion of the stirrer is such that a helical scan of the bed temperature is produced. Since the stirrer both rotates and reciprocates, the signals from the thermocouples are transmitted by an FM/FM telemetry system. The availability of the bed temperature signal makes it attractive as a means for determining the ash level. Thus, there is a need for a means of determining the ash level from the existing temperature signals from a fixed bed coal gasifier.